Vehicles are provided with closure members that are opened by lifting to provide access to the vehicle interior, such as lift gates, tailgates, deck lids, and the like. Power actuators are used to move such closure members at the push of a button on the dashboard, on a key fob, or by movement in front of a sensor. Power actuators generally include an electric motor and a gearing set that have sufficient torque to raise and lower the closure member. Alternatively, the power actuators may be hydraulic or pneumatic cylinders that have motor driven fluid pumps.
Torsion bars, air spring cylinders, tension springs, counterbalance struts, or other lift-assist mechanisms are used to reduce the load on the power actuator that is used to raise and lower the closure member. As power actuators are generally tuned off after opening to conserve battery power, while the lift-assist holds the closure open. Lift-assist mechanisms may be damaged, disconnected, or otherwise become ineffective for a wide variety of reasons.
Power actuators may have sufficient power to lift a closure member even if a lift-assist mechanism is disabled or broken. Under some circumstances the power actuator may not be able to hold the closure member in the raised position if the closure member is manually opened, if the lift-assist mechanism breaks, or becomes inoperative. The power actuator normally stops when the closure member is fully opened. The weight of the closure member may cause the closure member to close in an uncontrolled manner under the force of gravity after the motor stops.
This disclosure is directed to solving the above problems and other problems as summarized below.